Cystic fibrosis (CF) lung disease causes dehydration of the surface lining of the respiratory epithelium leading to mucostasis and chronic bacterial infection. The absent gene product in CF is the cystic fibrosis transmembrane conductance regulator (CFTR) protein that regulates fluid homeostatic mechanisms in the airway epithelium. We hypothesize that expression of functional CFTR in the airway epithelium of CF patients will restore CFTR function and thus normal lung function. Gene transfer strategies for CF lung disease have so far failed to show significant CFTR delivery to airway cells in vivo, primarily because the vectors did not efficiently transfer CFTR to the respiratory epithelium after intraluminal delivery. We have found that recombinant parainfluenza viruses (rPIV), infect cultures of human well-differentiated airway cells (HAE) with high efficiency after intraluminal delivery, and that gene transfer is specific to ciliated airway epithelial cells, the cell type requiring correction in CF. The high efficiency of gene transfer by rPIV to ciliated cells, the availability of recombinant versions of PIV and, the capacity to insert large transgenes into the rPIV genome suggests that these viruses may be useful for delivering CFTR to the ciliated airway epithelium of the CF lung. However, currently available PIV vectors are cytotoxic to ciliated cells. Therefore, we propose to generate novel recombinant rPIV-based gene transfer vectors that express human CFTR and test the efficacy and safety of these vectors at correcting the CF phenotype of CF HAE. We will also test the efficency, safety and the influence of the immune system on gene transfer by rPIV-vectors in the nasal epithelium of non-human primates in vivo. The Specific Aims of the proposed study are: 1) Can rPIV-Vectors be Generated for Efficacious and Safe CFTR gene transfer to Ciliated Airway Cells? 2) To Test the Efficacy and Cytotoxicity of rPIV-CFTR vectors on Human Well-Differentiated Airway Epithelial Cells In Vitro; and, 3) To Test the Gene Transfer Efficiency of rPIV-Vectors in the Non-Human Primate Nasal Epithelium In Vivo.